(1) Field of the Invention
The present invention relates to the compositions containing plant meristematic tissues.
(2) Related Art Statement
The breeding of plants has been conventionally achieved by fixing a superior characteristic acquired by crossing or the induction of mutation as a specific variety (fixed variety). In addition, techniques such as gene recombination and cell fusion have recently led to an employment.
However, anyone of the techniques requires, for particularly an annual plant, the process in which seeds are gathered from parent plants possessing a superior characteristic and these are sown in order to obtain offspring having the same characteristics as these parent plants. Such a breeding method with seeds requires much labor and time and a particular technique for producing a fixed variety and always involves the danger that the characteristics of the fixed variety once produced will deteriorate as a result of natural crossing.
When a useful variety is established as an F.sub.1 hybrid or obtained by a specific chromosomal pattern such as aneuploidy, heterozygosis of structural mutation, or triploidy, it is substantially impossible to cause certain characteristics to be inherited in the coming generation by seed propagation. In these circumstances, it is necessary to gather new seeds by crossing parent plants for each generation, or to obtain seeds by means of a particular treatment. These methods are complicated and, in some cases, involve the possibility of creating an extremely undesirable situation in that it is necessary to depend upon the supply of useful seeds from a particular institution.
Furthermore, propagation methods with seeds require much labor and time and involve disadvantage in being restricted by the weather and the type of land employed.
A technique of vegetative propagation has been developed for the purpose of overcoming the above-mentioned disadvantages, in which meristematic tissues such as somatic embryo, adventitious bud, shoot primordium, or callus which are obtained by culturing parts of the tissue of a plant body are further cultured to encourage shooting and obtain a plant body. Although in some cases this method causes a change in the number of chromosomes, by selecting the conditions, it is possible to obtain a clone having completely the same character as that of the original plant, whereby it is possible in principle to breed from one parent plant large numbers of offspring for several generations without limit.
However, natural seeds possess an embryo which later grows into an entire plant body, and botanical accessories such as an endosperm which becomes nutrient for the embryo and a seed coat for physically protecting the embryo. The botanical accessory serves to prevent the embryo from withering and germinating while in a state of preservation and to control the water content at a suitable level for the purpose of preventing decomposition. In contrast, meristematic tissues obtained by culturing tissue possess no botanical accessory of the type described above and are thus presented in a completely defenseless and exposed state.
The analogue of seed containing such uncovered meristematic tissues are disclosed in Japanese Patent Laid-Open Nos. 59(1984)-102308 and 60(1985)-118103. A subject matter thereof comprises the formation of the analogue of seed by encapsulating meristematic tissues in a gel matrix for the purpose of giving nutrients thereto.
However, such gel-encapsulation involves disadvantage in that the gel is difficult to handle and inferior in shelf life because of its low strength and the fact that it contains a large amount of water. In order to overcome this problem, a method of hardening the gel surface by a treatment with an agent such as glutaraldehyde is disclosed in the above-described Laid-Open Publications, but these offer an insatisfactory effect and are far from solving the problem.
In addition, faults are experienced since meristematic tissues are completely encapsulated in gel, so the tissues are insufficiently supplied with oxygen during germination and formation of root and are often hindered from growing and withered, and since the gel has large strength, so the gel is not broken and plumules are sometimes captured in the gel, depending upon the growing power of the meristematic tissues.